Where are they now? -- An Interview with KIPAC alum Justin Vandenbroucke

Apr 16, 2015

by Lori Ann White

In the series, "Where are they now?" we check in with KIPAC alumni: where they are now, how they've fared since their days exploring particle astrophysics and cosmology at the Institute, and how their KIPAC experiences have shaped their journeys.

Next up is Justin Vandenbroucke, who came west from colder climes for college and postdoctoral research opportunities, then returned to the frigid Midwest as an assistant professor at University of Wisconsin Madison. But even during his days in the balmy Bay Area, Vandenbroucke couldn't seem to stay out of the cold.

But we'll let him tell the story.

LW: To start, can you tell us a little bit about your background? Where you're from, where you went to school, what led you to KIPAC.

JV: I grew up near Chicago (in Evanston), then came to Stanford as an undergrad where I was a physics major with a math minor. I moved to Berkeley, where I worked on [the South Pole neutrino observatory] IceCube for my PhD in 2009 and then to KIPAC, where I was a Kavli Fellow from 2009–2012 and a NASA Einstein Fellow from 2012–2013.

It wasn't until I got to KIPAC that I remembered it had been established right around the time I moved from Stanford to Berkeley and at that time I had a glimmer of a thought that it would be fun to come back as a postdoc.

LW: Do you think your subconscious was taking care of you?

JV: To be honest when I first arrived I was intimidated by the level of discussion—so much of the cutting edge research we discussed was either done by people in the room or could be dissected expertly by people in the room. I overlapped with some amazing people at KIPAC—Rolf Buehler, Marco Ajello, Keith Bechtol, Stefan Funk, Markus Ackermann, David Paneque, Luigi Tibaldo, Matthew Wood—luckily I still collaborate with some of them.

By the time I left it felt more like part of the KIPAC family, and I had learned enough that I could contribute to the discussions. Some of my best memories are from during and after tea talks and paper discussions. They were a good way to catch up on research news and stimulate new ideas.

LW: What did you work on while you were at KIPAC?

JV: I stayed in touch with IceCube colleagues as a postdoc but I was really focused on gamma-ray astronomy. While at KIPAC I worked on a few projects analyzing data from the Fermi Gamma-ray Space Telescope and developing hardware in the lab for the Cherenkov Telescope Array (CTA), a ground-based project that will detect gamma rays using the Cherenkov radiation caused by showers of subatomic particles the gamma rays initiate when they hit the atmosphere.

JV: Fermi was built to detect gamma rays, which are electrically neutral. That's why we had to use the Earth's magnetic field—Fermi doesn't have a magnet to separate charged particles.

This figure shows how Justin and colleagues were able to use the Earth's magnetic field to differentiate between electrons and positrons by identifying their allowed regions around the Earth. This was a critical part of their analysis, since the LAT does not have a magnet of its own to allow distinguishing between these two types of particles of the same mass. (Image credit: Fermi LAT Collaboration)

That was fun because we stretched ourselves as much as we stretched the telescope. We learned a lot about the earth's magnetic field and used a detailed map of it developed by an international team of geophysicists, and we were able to confirm and extend the surprising measurement from the PAMELA satellite that the positron fraction increases at high energy. AMS is now continuing to improve and extend this measurement with high precision.

We still don't know what produces these excess positrons. With CTA we hope to measure the spectra at even higher energy, around and above 1 TeV. Now that I’m at UW Madison I’m combining neutrino astronomy and gamma-ray astronomy. It’s an exciting time for both! IceCube recently discovered the first high energy astrophysical neutrinos, so we are busy trying to characterize them and understand where they come from.

This artist's rendition of CTA at night shows how a cosmic ray which initiates a shower of charged particles in the atmosphere that then each emit Cherenkov radiation in a small cone, which then all coalesce into a larger glowing blue cone. This can then be detected by special instruments like the telescopes of the planned CTA. (Image credit: DESY/Milde Science Comm./Exozet).

LW: Do you have a favorite experience doing fieldwork, as well?

JV: During my PhD I worked at the South Pole during three seasons to help build IceCube and to run a side project for my thesis. It’s an incredible place, and being part of the construction team for such an ambitious project in that environment is certainly one of the high points of my life. My uncle used to make fun of me because he thinks I chose a particle that’s so hard to detect that I had job security and could continue traveling to exotic places, as long as we didn’t find them. Of course now that we found astrophysical neutrinos we will work even harder to detect more of them!

I had an undergraduate research project listening for neutrinos at a deep underwater Navy site in the Bahamas. That was also a great experience. To install and calibrate our experiment, I worked on a tiny island whose only inhabitants were three old Navy guys—a radar specialist, a cook, and a commander (to command the cook, the radar guy, and the physics student). Of course as in many physics projects, it involved a lot of time in a windowless room programming. But I also got to drop calibration sources off a boat, hack a mangrove swamp, and wade out in the water until a shark scared me back to shore.

Now I’m spending some time at the VERITAS site in Arizona—VERITAS is a precursor to CTA. We’re on a big push to construct a new prototype for CTA telescopes there in the next year, and I’m helping lead the camera for that.

I think if I hadn’t been a physicist I would have done geology or some other job that involves fieldwork. That’s one of the things I love about particle astrophysics—we use creative techniques that often require fieldwork in fun places.

LW: Now that you're a professor, what would you tell undergraduates to help them prepare themselves for a place like KIPAC?

JV: The first thing is to figure out if you like research. It can be a roller coaster—frustrating and tedious sometimes, thrilling other times. The good thing is that the best way to both prepare for grad school and to decide if you want to go to grad school is to get involved in research, especially during the summer.

Also, find a good mentor. [Stanford physics professor] Giorgio Gratta mentored me during the Bahamas project. That experience showed me how much fun research can be, especially in particle astrophysics.

LW: Now that you're a professor yourself, how do you like teaching?

JV: Postdoc life was a special time, particularly at KIPAC—having the time, resources, and academic environment to be fully focused on research. But I’m enjoying being back in the classroom. It’s fulfilling in a way that research is not. So far I’ve taught an undergraduate course for non-science majors on the physics of energy production and climate change, and an advanced graduate course on experimental methods in nuclear, particle, and astro-physics.

LW: I understand you're involved in a project that turns cell phones into cosmic ray detectors, which sounds very cool. Can you tell us more about it, and how to convert our own cell phones?

JV: It's called the Distributed Electronic Cosmic-ray Observatory and it started at KIPAC with a teacher named Levi Simons I mentored one summer through the STEM Teacher and Researcher program. The basic idea is that camera image sensors on cell phones can be used to detect photons but also to detect ionizing radiation (from cosmic rays or background radioactivity). The user pool is growing quickly all over the world and the data are automatically synced to a central database where users can analyze the data.

We think it is a great way for students and other interested people to get engaged in particle physics, nuclear physics, and astronomy by turning the devices they already use so much into particle detectors.

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